Formation of a string and pool topography as expressed by morphology, stratigraphy and current processes on a mire in Kuusamo, Finland

Abstract

A review is made of earlier work and theories on a formation of string mires, together with a report on detailed investigations carried out over seven years on a small string (aapa) mire in eastern Finland, to determine the applicability of earlier hypotheses on the explanation of string and pool patterning. Attention is paid to the topography of the surface and bottom of the mire and to the peat and pollen stratigraphy. Results are presented of year‐round temperature measurements and long sequences of snow and frost depth readings from both pools and strings. Snow depth is shown to be a decisive factor in ground frost formation. The strings are shown by a series of repeated Geodimeter measurements to move partly upslope, partly downslope and partly in a sideways direction. The maximum cumulative movement recorded was about 1 m in seven years. Some of the pools remained unfrozen even in midwinter because of groundwater flow. Uneven retention and discharge of the surface water causes the strings to be in a labile state and promotes their movement. The initial formation of the string and pool topography is dated to 2,000–3,000 radiocarbon years B.P. and attributed to a rise in the groundwater table due to climatic change. The resulting fluviodynamics of the mire surface led to the accumulation of loose material into ramparts at the spring flood season and led in time to differential peat formation conditions, progressive peat accumulation on the strings, and regressive peat degradation in the pools. Thus the strings became higher and the pools deeper. The authors believe the importance of frost action, ice expansion and solifluction on the development of string and pool patterns is frequently overestimated.

Linking habitat modification to catastrophic shifts and vegetation patterns in bogs

“…The origin of string and flark patterns has received considerable attention during the last century (Charman 2002), which has resulted in many hypotheses involving physical and biotic processes to explain the development of this peatland patterning (Seppäla and Koutaniemi 1985;Glaser 1992;Belyea and Lancaster 2002). We restrict our discussion to biotic processes since these are currently thought to be governing peatland patterning (Seppäla and Koutaniemi 1985;Charman 2002).…”

“…Other studies focus on the initiation of strings, emphasizing the importance of spring floods in string formation (Sakaguchi 1980;Seppäla and Koutaniemi 1985). During these floods slush and plant remains are transported toward elevations on the mire surface, thereby amplifying the surface microtopography.…”

Regular Surface Patterning of Peatlands: Confronting Theory with Field Data

“…Finally, some studies focus on the possible role of spring floods in pattern formation (Sakaguchi 1980;Seppä la and Koutaniemi 1985). During high water levels, as occurring with spring snowmelt, storage capacity in the hollows may be insufficient so that water can flow freely over the ridges (for example, Quinton and Roulet 1998).…”

The role of inter-specific, micro-habitat and climatic factors on the carbon isotope (δ13C) variability of a modern leaf assemblage from northern Scandinavia: implications for climate reconstruction

“…The role of micro-habitat (hummock/hollow) on carbon isotope discrimination There has been significant debate relating to the development, climatic significance and temporal stability of hummock/hollow microtopography on plant growth and the impact of its variation through time upon the consistency, bias and reliability of the resulting palaeorecord (Walker & Walker 1961;Barber 1981;Seppäla & Koutaniemi 1985;Barber et al 1994;Korhola 1995;Karofeld 1998;Nilsson et al 2001). Although this discussion mainly relates to hummocks and hollows on mire surfaces, general geomorphology and associated differences in for example moisture availability may also impact on plant physiology and leaf/needle isotope values.…”